So if I'm interacting with other users' devices, why am I paying $10/month? This seems like a great (nay, genius) idea if you just buy a device that accepts a

So if I'm interacting with other users' devices, why am I paying $10/month? This seems like a great (nay, genius) idea if you just buy a device that accepts a standard 3.5 inch HD, half the space is yours, half is for distributed backup, no monthly fees, just the upfront $ for the box itself..